The facet joint is an articulating joint of a spinal motion segment that can degenerate during aging, trauma, typical use and other factors. The facet joints in various regions of the spine are oriented in different planes, for example, the lumbar facet joints are generally located in the sagittal plane SP, the thoracic facet joints are generally oriented in the coronal plane CP and the cervical facet joints are generally oriented in the axial or transverse plane AP (FIGS. 1 and 2). These orientations facilitate different types of motion in the respective regions of the spine.
Degenerated facet joints are often painful as a result of, for example, wear between two arthritic articulating surfaces that surround the synovial joint capsule. The surfaces of the facet joints are covered by articular cartilage. Inflammatory reactions may occur when the cartilaginous surfaces of the facets become degraded or fissured, thereby leading to direct bone-on-bone contact and resulting in pain. Over distraction of the surrounding joint capsules may also cause pain to the patient. Patients typically undergo a fusion surgery to alleviate this pain.
It is desirable to develop an implant for insertion into the facet joints between adjacent superior and inferior vertebrae to alleviate pain resulting from degenerating facet joints that may not result in immediate fusion of the facet joint.